Project Summary This project is designed to remedy unaddressed and interlocking HIV-prevention and mental health needs among gay and bisexual men (GBM) in the Central Eastern European country of Romania, and their underpinning stigma-related mechanisms. Rampant stigma contributes to the increasing prevalence of HIV among Romanian GBM (from under 10% in 2009 to close to 20% in 2014, by best available estimates) and keeps GBM out-of-reach of HIV-prevention services. Our mHealth pilot intervention (titled ?Despre Mine. Despre Noi.? [DMDN] translated as ?About Me. About Us.?), which reduced US and Romanian GBM?s risk for HIV infection while also reducing depression and alcohol abuse in initial pre-post trials, is now ready for testing in a randomized controlled trial with a large national sample. The DMDN intervention entails eight 60-minute live chat sessions delivered by trained counselors on our mobile study platform using motivational interviewing (MI) and cognitive-behavioral skills training (CBST). First, during pre-trial (mos 1-5), in collaboration with a community advisory board consisting of GBM community members, GBM-affirmative physical and mental health providers, and our technical developer, we will fine-tune the DMDN intervention based on our pilot findings and evaluation interviews, and expand the original DMDN education materials for an education attention condition (EAC) that will serve as our control. Second, during the intervention phase (mos 6-45), we will recruit, screen, assess, and randomize GBM at risk for HIV infection and alcohol abuse to either the DMDN intervention (n=163) or EAC (n=163). The conditions are content matched, and both are hosted on our study platform. While DMDN will consist of eight weekly mHealth live chat sessions, EAC will consist of eight self- administered educational modules. Third, during the follow-up phase (mos 8-55), we will assess at 4, 8, and 12 months post-baseline, in a mobile fashion identical to the baseline, the primary outcome of condomless anal sex with male partners and secondary outcomes of alcohol abuse, depression, biologic HIV/STI infection, HIV/STI testing, and psychosocial mechanisms rooted in the Information-Motivation-Behavioral Skills (IMB) model (e.g., HIV/STI knowledge, condom use self-efficacy) and minority stress theory (e.g., identity concealment, internalized homophobia). We hypothesize that 1) compared to GBM randomized to EAC, those randomized to the mHealth DMDN condition will report significant reductions in condomless anal sex across the 12-month follow-up, 2) IMB and minority stress mechanisms will statistically mediate intervention efficacy, and 3) compared to EAC, the DMDN intervention will prove cost-effective in terms of HIV infections averted and reduced depression and alcohol abuse. If efficacious and cost-effective, DMDN presents a highly disseminable intervention that could significantly prevent HIV infection among GBM in high-stigma, low- resource areas, where GBM are disproportionately affected by HIV, yet kept out-of-reach of brick-and-mortar prevention services.